Running Amok: Why Are Virtually All Spree Killers Men?

After the recent Sandy Hook Elementary School massacre of innocents, a friend of mine posted this question to his Facebook page: "Once again, we miss the obvious... It is boys and men who shoot, not girls and women! Mental illness aside... what is it about boys, men, and masculinity?"

In their 1988 book Homicide, Martin Daly and Margo Wilson defined this type of rampage killing as a "...frenzied homicidal rampage until (the killer is) killed or subdued." They too asked: " ...why don't women do the same?" (p. 156) in chapter 7 of their book, which is aptly titled Why Men not Women?

Here is a partial list of school spree killing massacres from a Wikipedia article—as ranked by the number killed. Note that all of the perpetrators are male, and that most of them committed suicide at the end of their rampage. With two exceptions, the killers were in their twenties, or younger.

A similar pattern is found in spree killings in cultures around the world. The table below lists spree killers in Asia. This top portion of the list is from the Wikipedia article, List of Rampage Killers, which also lists spree killers from various regions around the world. Again, we see the same general pattern: the spree killers are virtually always male, in their twenties or teens, and they most always end their spree by committing suicide, or they are killed by police.

List of Rampage Killings in Asia (from Wikipedia)

The fact that spree killing occurs in all cultures, albeit rarely, and the fact that it is a strongly sexually dimorphic phenomenon, are rather ominous indications that it is not simply the result of some type of cultural fluke (such as a "spree killing culture" operating on a blank slate mind/brain). Instead, these facts suggest that it is a rare manifestation of some aspect of human nature. In particular, male nature.

Spree Killing Is a Cross Cultural Phenomenon

The Young Male Syndrome

Daly and Wilson (1988) noted that spree killing (also called running amok, rampage killings, or "going postal") is a rare phenomenon, but when it happens the perpetrator is virtually always male. This suggests that it is a manifestation of a sex difference of the greater general male tendency toward physical violence. Someting happens to males at about age 14 that doesn't happen to girls. The sex difference in committing homicides really starts to explode on the graph (see the graphic). From age 14 onward, the rate at which males begin to murder others begins to far outstrip that of females. It peaks when males are in their mid-twenties, and then it starts to decline. Although the graph is based on Canadian data, this same general pattern with respect to the sex and age of murderers is seen around the world. Even in cultures widely separated in space and time, the graph looks pretty much the same.

Homicide Rate by Age and Sex (Daly & Wilson, 2001)

What would motivate anyone to start killing innocent strangers, often for no apparent reason, is beyond the ability of most of us to fathom. Our empathy is for the victims; we feel deep disgust, anger and contempt toward the perpetrator. His actions seem impossible to understand.

However, researchers and policy makers at some point must step beyond their own feelings of disgust and outrage to try to understand why this happens. A good scientific understanding of what causes someone to "go postal" may eventually help professionals to better identify any early warning signs. They may be able to develop interventions for individuals who may be close to the edge of running amok. And, a sophisticated understanding of the phenomenon will also shed light on these sex differences: Why men, not women? Why predominantly young men? Why does the spree typically end with suicide (or "suicide by cop")?

Human Nature: The Puzzle of Spite

In most all interactions with someone else, both you and the other person can either gain or lose from the encounter. From an evolutionary perspective, selfishness, altruism toward genetic kin, and reciprocity with non-kin make sense—all can help you to propagate your genes into the next generation (which increases your inclusive fitness—the "bottom line" in the scorecard of evolution).

But why does spite exist? Spite occurs when both you and the other person lose from an interaction. As noted by Richard Dawkins in his classic book The Selfish Gene, initially the existence of spite appeared to be something of an evolutionary puzzle. Why would anyone engage in spite, and hurt themselves by doing so?

Spree killing is an extreme example of spite. As noted earlier, the killer himself virtually always dies at the end of the rampage.

And, on a far lesser scale, ask yourself this question: Have you ever done something out of spite—something that you did on purpose to hurt your target, but, that also hurt you? Most of us have done something spiteful at some point in our lives. The motive is typically revenge—to redress some perceived injustice against us, even if we hurt ourselves further in the process.

The Dark Side of Human Nature: The Relativity of Inclusive Fitness

There is a dark side to evolution that allows for behavioral predispositions for spite to remain in the gene pool.

If evolution "wants" you to copy as many of your genes into the next generation, having a lot of children is the obvious solution. However, inclusive fitness is relative, not absolute. That is, nature doesn't "say" (absolute inclusive fitness): "Have 2 kids (or help 4 full sibs), and then you can stop. Good job! You did your genetic duty, and you may pass along now..." Instead, nature "says" (relative inclusive fitness): "Out-reproduce your competitors. Your competitors are all of the genes in your species' gene pool that you do not share. If the average inclusive fitness score is 4, then you go for 5... " In other words, our psychological adaptations are designed to not just "keep up with the Joneses" but to genetically "do better than the Joneses."

Now, here is where the nasty part of nature, including human nature, comes in. An unfortunate corollary of the relativity of inclusive fitness is that an organism can also increase its inclusive fitness by reducing the inclusive fitness of others. Reducing the proportion of others' (non-kin) genes in the gene pool will increase the proportion of yours. That potentially makes murder, genocide, warfare, and other nasty stuff potential relative genetic pay offs. This suggest that human nature includes some nasty psychological adaptations that, when triggered by certain circumstances, can result in homicidal behavior, including spree killings.

Why Is Male Nature More Homicidal Than Female Nature?

Brief answer: because in an evolutionary sense, males are more desperate.

As I noted in that post, there are two groups of men for which there are no female equivalents: males who are "reproductively disenfranchised" (excluded by the opposite sex from reproduction) at the low end of the distribution, and males who win a "reproductive jackpot" at the high end (produce many offspring—the documented world record number is 888 children sired by one man).

However, at the low end, there are indeed some men with whom no woman would want to risk a pregnancy. Some men are just so unappealing (unattractive, stupid, poor, in poor health, and apparently with lousy genes) that no woman would want to have sex with him. No woman would choose that man to be the father of her children. Imagine a homeless man, empty whiskey bottle in hand, sleeping in a urine stained cardboard box. Any takers? These guys are not happy campers. They are losing out in the most important biological game of life.

Many spree killers fall into this category, or, they so perceive themselves. Spree killings often follow a personal rejection by a female(s), and, the perception that more rejections are likely to follow perhaps due to social ostracism or loss of social status. Daly and Wilson (1988, p. 280) note that "The most common precipitating events are difficulties with wives or girlfriends, losses of face, and losses of money..."

Male Paternity Insecurity: Mommy's Babies are Daddy's Maybes

Another evolutionary challenge for human males is that, unlike women, men have never been absolutely certain whether a particular child is genetically their own (with the modern exception of DNA paternity testing that is available today). In contrast, women never have had such doubts. Any child they bear is certainly her genetic offspring. This sex difference also extends to extended genetic relatives—we are more confident that the offspring of our female, rather than male, relatives share our genes. Thus, women typically perceive that they have genetic kin who could benefit from their assistance. This may help to explain the sex difference in suicide rates.

The Male Suicide Rate is 3 to 4 Times The Rate for Women

As noted earlier, spree killings most often end with suicide (or "suicide by cop").

One evolutionary theory of suicide is that it is more likely to occur when a person feels that their future prospects are extremely bleak, they feel ostracized and isolated, and they perceive that they are a net burden on genetic relatives (thus reducing their relatives' inclusive fitness). Several factors may help to provide ultimate (evolutionary) explanations for the higher rate of male suicide: (a) male paternity uncertainty, noted above, may result in males feeling less of a connection to putative genetic relatives, and (b) more males than females are at the lower end of the reproductive variance distribution (i.e., "reproductively disenfranchised") such that their perceived future prospects are dismal.

Male Tribal Warfare: Violence Between In- vs- Out Groups

Virtually all spree killers are men, and virtually all tribal and national warfare combatants are, and have been, male. Some rampage killers may perceive that they are embedded in and surrounded by members of a hostile out-group "tribe."

Daly and Wilson (1988, p 280) noted that:

The young man who runs amok is typically residing far from home, often for the first time in his life. He has typically been brooding over failure. One cannot but wonder if his psychology is that of a doomed warrior, surrounded by enemies and determined at least to inflict some costs upon them.

Rampage Killing as a Manifestation of Sexually Dimorphic Psychological Adaptations

So, why men, not women? We may now have some possible answers.

A spree killing may be an act of extreme spite that decreases the relative reproductive success of non-kin competitors by killing them (especially members of an out-group "tribe"), and thus increases the relative inclusive fitness of the killer's genetic kin. Also, the suicide of the killer may decrease real or perceived burdens on his genetic relatives due to his perceived low status and dismal future reproductive prospects. In ancestral environments, being ostracised or ejected from one's tribe could amount to a death sentence. Exacting retribution against the perceived injustice of group ostracism may also be a contributing motive.

In general, males may be more predisposed toward violent conflicts ultimately due to their greater reproductive variance (the foundational evolutionary pressure behind the evolution of male psychological adaptations for greater risk-taking, violence and status seeking). Male low levels of assurance of genetic parentage may exacerbate their self-perceived poor reproductive prospects, which may further increase already high intrasexual competition pressures.

Of course, this is a cold technical analysis that doesn't fit with well with our daily "folk psychology" conceptions of human behavior. And, some of these explanations may seem about as non-intuitive as quantum physics. But, as with quantum physics, it is the underlying mathematics, the foundational theory, and the level of empirical corroboration that may help us to develop a sound scientific understanding of rampage killing—a horrifying and otherwise deeply puzzling phenomenon.

If we are to have a realistic hope of reducing the darkest aspects of human behavior we must first be willing to face, and then work to develop an accurate scientific understanding of, the deep evolutionary forces that have molded and that underlie human nature.

It's not just men but predominantly white men. It's as if tehy feel society owes them something, due to some sort of race priviledge and when they feel disenfranchised, life not going as they expected, someone or something peeved them off for the last time, then they go on a shooting spree. I'd like to see some research about white males and mass killing sprees.

It's not just men but predominantly white men. It's as if tehy feel society owes them something, due to some sort of race priviledge and when they feel disenfranchised

Quite the opposite. It's precisely because our society does NOT grant any special privilege to whites (nor should it), but expects us to make it on our own -- and also tells us, that we are not discriminated against or disadvantaged in any way whatsoever. Thus, if a white male fails, he has NOBODY to blame but himself. The judgement of failure versus success is made by the harshest jury of all: white women. I've yet to hear of a spree killer who had a wife and kids waiting for him at home.

Blacks and Latinos, by contrast, always have the psychological fallback of blaming a "raciss" society, and can suffer failure, or not even bother trying, without damage to their pride. And the women of their community don't seem to care, either -- poor blacks and Latinos don't seem to want for female attention.

As a result, white failures usually kill THEMSELVES. White males have a vastly higher suicide rate (and nobody seems to care). Sprees are very rare statistically, and even they usually end in suicide. Whereas black and Latino failures, become criminals and lash out at society. Both categories are taking revenge on those whom they blame for their failures.

white failures usually kill THEMSELVES... Sprees are very rare statistically, and even they usually end in suicide

... May I also note, that most sprees seem to bear some psychological relation to the shooter's perceived failure? School shooters were usually severely bullied; hence a schoolyard is seen as "enemy turf". (But why kill innocent kids; why not show up at the 10 year reunion and kill your actual tormentors?? This, I admit, I don't get.) Workplace shooters are usually recently fired or otherwise feel unjustly treated there. At least guy whose whole life had been ruined by tax problems, killed himself and tried to kill many others by crashing a plane into an IRS building.

But most white men who want to die, blame ONLY themselves, and kill only themselves.

The probability of European-Americans commiting serial murder (which in the FBI publication I link to includes spree killing) compared to their percentage of the population is no greater than that for other races.

The only difference is that European-Americans are more likely to commit serial murder per capita than they are to commit other crimes. But don't worry, in those other categories of crime, African-Americans are more than capable of picking up the slack for European Americans.

" Serial murder lends itself nicely to the analytical methods developed here provided suitable data are available. Only a few systematic accounts of the race and ethnicity of serial killers exist. There is an exhaustive study of African American serial killers (Homicide Studies 2005; 9; 271) by criminologist Anthony Walsh, and also Eric W. Hickey's book, Serial killers and their victims, Brooks/Cole, 1997. That's about it.

Walsh identified 90 African American and 323 white American serial murderers, all men operating between 1945 and 2004. (Though Asians, Hispanics and Native Americans were not included in the study, their addition would not alter the fact that most serial killers are white men.) African American serial killers made up 22% of Walsh's sample, a figure in close agreement Hickey's enumeration. But, as blacks number well below 22% of the U.S. population, they are actually overrepresented among the ranks of serial killers -- roughly by a factor of 2."

"The racial demographics regarding serial killers are often subject to debate. Compared to the United States and South Africa, Australia has a much lower incidence of known serial murders.[11] In the United States, the majority of reported and investigated serial killers are white males, from a lower-to-middle-class background, usually in their late twenties to early thirties.[6][12][13] However, there are African American, Asian, and Hispanic (of any race) serial killers as well, and, according to the FBI, based on percentages of the U.S. population, whites are not more likely than other races to be serial killers.[13] Criminal profiler Pat Brown says serial killers are usually reported as white because the media typically focuses on "All-American" white and pretty female victims who were the targets of white male offenders, that crimes among minority offenders in urban communities, where crime rates are higher, are under-investigated, and that minority serial killers likely exist at the same ratios as white serial killers for the population. She believes that the myth that serial killers are always white might have become "truth" in some research fields due to the over-reporting of white serial killers in the media.[12]"

If you believe that there would be no (or much less) war if women were in charge, you are delusional. States do not behave like men or like women, but like states. Warfare between states is not the result of a defect in masculinity, but rather competition over scarce resources and cultural incompatibility. Blaming men for warfare is an attempt to give a simple explanation for a very complex phenomenon.

I don't have to be a historian to know that I've a right to bear arms for personal self defense ... the Second Amendment guarantee individuals the right to carry firearms outside the home for self defense and other lawful purposes ... There is so many insane ppl around ... and yes, there're communities that deal with the threat of gun violence every day of their lives but when tragedies happen then ... we realize something must be done. So, let's talk about guns ... gun violence ... and criminal's mental health ... and have on mind, taking my gun away will not stop deranged individuals committing monstrous crimes. And globally there're crazies everywhere... The major difference is that they don't have so easy access to guns like we do here in US. And the NRA should really more represent gun owners then gun manufacturers ... and if the reality is any indication ... the only thing that will come out of this last tragedy is gun sales will go up ... All states require a simple test to show proficiency to drive a car ... so if the same standards are implemented and requested from CC permit applicants as the ability to responsibly handle a firearm, then nobody will advocating taking away weapons if we show we can responsibly use the thing... I'm for banning assault weapons or limiting the size of ammunition reloaders and mainly making it harder for mentally unstable people to get guns ! ... and if more sane people were armed, the crazy people would get fewer shots off ... this is my personal opinion and everyone can help by donating to mental health research and institutions instead of pointing to gun control as the problem ... CC permit applications and issuing increases while violent crime and murder rates decreases in some part of the CA and all around the States ... Of course we would never see the mainstream media report this ... The presence of guns don't make a country violent.... A violent ppl and culture do ... a culture of violence, particularly a culture of gun violence that pervades American society...
Coco Chantrenne, M.B.A., Ph.D

Lanza killed his mother. Kip Kinkel killed both parents. If this is a common pattern, it would seem to bely at least some of the explanations Mills gives, such as reducing burden on family members and increasing relative reproductive fitness (which would surely be reduced by killing close genetic relatives, who might go on to have further children or at least provide support for the killer's genetic line).

Don't have an answer, just curious how this might be explained if it is indeed common.

Humans far more disproportionately kill non-relates over relatives. And this effect is generally linear -- the more genetically related the less likely is homicide, despite the fact that we generally tend to spend more time around close relatives than non-kin. As Daly and Wilson note in their book "Homicide" "...otherwise equivalent conflicts will tend to be increasingly severe and dangerous the more distantly [genetically] related are the principals." (p 34)

Another factor that might be related, as noted in my post, is that due to paternity uncertainty, males are less likely to have full confidence of who their genetic kin actually are, and this may contribute to the sex differences in running amok and homicide of kin.

I believe I read that women are far less likely to kill or be killed...but when they're killed, it's usually by a domestic partner, and when they kill, it's usually familial.. (ie male violence usually being amongst strangers, female violence being amongst kin)
Thoughts?

While the majority of spree killers are male (especially school spree killers) there is one case that I know of where a female committed a school spree killing. She lived across from the school and one day while kids arrived to school she opened fire. I can't remember her name but she was only like 14 or so. Also she didn't commit suicide or killed by cops. She went through trail and sentencing.
This article does raise very good questions though. The most interesting one being why are most spree killers males around 14 to 25 years old. Is it mainly hormonal? Or are there other social reasons why?

Thank you for this fascinating article. In your research, did you come across the psychiatric diagnoses of any of these spree killers?
Sometimes this information comes out / gets published after the incident, unless the shooter was killed (or committed suicide) after the event. The psychiatric diagnosis is more likely to become public if the shooter goes on trial.

If you have information regarding the formal psychiatric history/diagnosis of any or all the spree killers you listed, would you share it?

I'd like to add: since age 14 is the average age for puberty onset in males, and since male hormone levels peak in the early to mid-twenties, then testosterone levels probably are a key factor in generating the spree-killer phenomenon.

Since the beginning of time men have been celebrated for being aggressive and violent. It became a portrait of masculinity. I work with mostly men and they mock men who appear to have feelings or compassion. They say it's handing over their man card. Women on the other hand are criticized and ostracized by society and their peers for being aggressive or violent. Women also correct other women when we see a behavior that is not right. I've seen men applaud other men for mistreating their wives, girlfriends, being rough, and unfeeling. Our culture has something to do with this. And we never address the fact that some people are just evil. They kill people because there is evil in them. Blame it on genes if you must, but there are evil people in the world. My aunt is a social worker and she had two 5 year old boys who were already showing sociopathic behavior. One killing animals and hiding them in closet. The other threatening his parents with knives. Murder is evil. We can blame the mental health of a person or call it what it is...pure evil. Those who take the lives of the innocent are operating under an influence of evil and we have in movies and in culture glorified the men who are violent, take what they want, have no feelings or compassion, and we wonder why we have more men in jail than women. We then wonder why men kill more than women. We wonder why men rape, commit hate crimes, etc...we have set a cultural standard that says part of being a man is not having compassion. Until we change that, we can expect to keep producing men who don't care about anyone but themselves.

I am puzzled why you say that being "reproductively disenfranchised" only happens to men, that there is no female equivalent. Surely there are women too who are very unattractive, have addictions, sleep in cardboard boxes etc who are unlikely to find a sex partner? Just as there are male virgins who would rather not be, there are female ones. Yet that disenfranchisement does not lead to spree killings.